I've been Google'ing, and it looks like there are some events, like this one in the Application Log:
https://support.microsoft.com/en-us/kb/921471
Or these:
Get help with activation errors - Windows Help
But I can't find a comprehensive list of the errors. Presumably, if the Agent was installed, you could look for these messages in the log history to see if Activation had issues, but the LEM isn't going to do inventory reports on activation status.